1. Field of the Invention
The present invention relates to a CVD film formation method using high-density plasma.
2. Description of the Related Art
In addition to achieving a detailed pattern (hereinafter referred to as xe2x80x9cmicropatternxe2x80x9d) for semiconductor integrated circuit elements, it has become essential to ensure that high-aspect ratio interwiring spaces are filled using interlayer insulating film without the generation of voids, or that interwiring capacitance is reduced using a low-dielectric constant film so that wiring delay is reduced. For this reason, a high-density plasma CVD (chemical vapor deposition) technique has become essential, by which method not only is it possible to perform film formation and Ar sputtering etching simultaneously, and to improve filling characteristics of the insulating film or the like, but an insulating film of high quality can also be formed which is doped with fluorine in order to obtain low dielectric constant.
FIG. 4 is a schematic cross-sectional view of a high-density plasma CVD device. This CVD device is a leaf-type CVD device in which semiconductor substrates are processed one at a time. An electrostatic chuck 3 is provided, whereon a semiconductor substrate 2 to be processed is placed, inside a reaction chamber 1.
Components connected to this reaction chamber 1 are: a reactive gas supply line 4; a cleaning gas supply line 5; a main exhaust line 8, which has a exhaust valve 6 placed thereon and which is connected to a dry pump 7 at one end; and a rough exhaust line 11, which has a exhaust valve 9 and a throttle valve 10 placed thereon and which is connected to the dry pump 7 at one end on the side the throttle valve 10 is placed.
An applicator 12, which changes cleaning gas to plasma, is placed on the cleaning gas supply line 5. A throttle valve 13, a gate valve 14 and a turbo pump 15 are placed on the main exhaust line 8, between the reaction chamber 1 and the exhaust valve 6, in this order from the reaction chamber 1 side. The turbo pump 15 is used since reactive gas can thus be exhausted in the course of the formation of a CVD film and, further, a considerable vacuum can thereby be achieved in the reaction chamber 1, and also since a turbo pump currently constitutes the only means of fulfilling such conditions.
A process of forming a CVD film, which utilizes the above-mentioned high-density plasma CVD device, will be described hereinbelow with reference to the flow chart of FIG. 5.
First of all, at #400, with the gate valve 14 of the main exhaust line 8 closed, while 1100 sccm of nitrogen trifluoride (NF3) is being introduced from the cleaning gas supply line 5, the pressure in the reaction chamber 1 is controlled to be a high pressure of 3 Torr by way of exhaustion via the rough exhaust line 11, which is at a low vacuum and is connected to the dry pump 7, so that cleaning is performed inside the reaction chamber 1. The path, along which NF3 flows, runs in the following order; from the applicator 12 to the reaction chamber 1, the exhaust valve 9, the throttle valve 10 and the dry pump 7.
Next, at #401a, reactive gas, which is a mixture of monosilane (SiH4), oxygen (O2) and argon (Ar), is introduced from the reactive gas supply line 4, and the pressure of the reaction chamber 1 is controlled to be 6 m Torr. In other words, with the exhaust valve 9 of the rough exhaust line 11 closed, reactive gas is introduced from the reactive gas supply line 4, and, the gate valve 14 of the main exhaust line 8 is opened, the turbo pump 15 is driven, and by adjusting the speed of exhaustion by means of the throttle valve 13 and by way of exhaustion via the main exhaust line 8, the above-mentioned pressure value is maintained. At this time, the rotation speed of the turbo pump 15 is 30000 rpm. Under these conditions, electrical power is applied to the reactive gas inside the reaction chamber 1 by a high-frequency power source (not shown in the figure) to produce high-density plasma, whereby a CVD film is formed on a semiconductor substrate 2. The path, along which reactive gas flows, runs in the following order; from the reaction chamber 1, the throttle valve 13, the gate valve 14, the turbo pump 15, the exhaust valve 6, and to the dry pump 7.
Thereafter, at #401b, similarly to #400, while 1100 sccm of NF3 gas is being introduced from the cleaning gas supply line 5, the pressure in the reaction chamber 1 is controlled to be 3 Torr by way of exhaustion to the rough exhaust line 11, and cleaning is thus performed inside the reaction chamber 1. The path, along which NF3 flows, runs in the following order; from the applicator 12 to the reaction chamber 1, the exhaust valve 9, the throttle valve 10 and the dry pump 7.
Further, steps #401a and #401b constitute one cycle for one semiconductor substrate 2, therefore, by the repetition of 50 cycles, from #402a, #402b . . . to #450a, #450b, a CVD film is formed on fifty semiconductor substrates 2.
However, a problem exists with the conventional CVD film formation method mentioned above in that, irrespective of whether cleaning of the reaction chamber 1 is performed using high-pressure NF3 each time the formation of a film on one semiconductor substrate 2 is complete, a great many particles are produced that cause unsatisfactory formation of a micropattern on the semiconductor substrate 2, and in that the yield of a semiconductor device is therefore dropped.
It is an object of the present invention to provide a CVD film formation method, as a means of resolving the above-mentioned problems, that is capable of reducing the production of particles which are the cause of unsatisfactory formation of a micropattern on a semiconductor, without causing a drop in productivity, and that is capable of improving the yield of a semiconductor device.
According to a research by the present inventor, et al., the production of particles is caused by the exhaustion of cleaning gas NF3via a rough exhaust line. This rough exhaust line is utilized to avoid a rise in temperature of a turbo pump as a result of flowing high-pressure cleaning gas in the main exhaust line that comprises this turbo pump, thereby to avoid deformation or the like of the blades of a turbo pump and occurrence of breakdowns thereof. However, because of this, no cleaning gas is made to flow in the main exhaust line, providing no opportunity to remove, by etching, reactants (mostly SiO2 when the high-density plasma CVD film is an insulating film) which are accumulated within the gate valve and the turbo pump. This causes production of particles of the reactant which are then caused to adhere to the semiconductor substrate during the formation of a film.
For this reason, according to the present invention, in a state in which the cleaning-gas pressure is made low, or the rotation speed of the turbo pump is made low, cleaning gas is made to flow in the exhaust line that comprises the turbo pump such that the reactant adhered to this exhaust line may be removed.
In other words, the present invention is characterized in that upon forming a CVD film on a plurality of semiconductor substrates by using a CVD device that comprises a reaction chamber for forming a CVD film, a first exhaust line which is connected to the reaction chamber and does not include a turbo pump, and a second exhaust line which is connected to the reaction chamber separately from the first exhaust line and which includes a turbo pump, two processes are performed, namely, a first process, which is repeated a number of times that corresponds to a predetermined number of substrates, and which comprises: a step of introducing a semiconductor substrate into the above-mentioned reaction chamber to form a CVD film thereon and, removing the semiconductor substrate, whose film formation is completed, from the chamber, in a state in which, while reactive gas is being supplied to the reaction chamber, the turbo pump is driven to exhaust the reactive gas via the second exhaust line such that the chamber is held at a predetermined internal reaction pressure; and a step of performing low-pressure cleaning of the reaction chamber, from which the above-mentioned semiconductor substrate has been removed, by, while supplying cleaning gas to the reaction chamber, discharging same via the second exhaust line such that the chamber is held at a predetermined low internal pressure that is higher than the pressure during the film formation, and a second process in which high-pressure cleaning of the inside of the reaction chamber is performed by, while supplying cleaning gas to the reaction chamber, discharging the gas via the first exhaust line such that the chamber is held at a predetermined high internal pressure that is higher than the pressure during the above-mentioned film formation. The second process for the high-pressure cleaning using the first exhaust line is implemented at least before or after the first process.
Further, the CVD film formation method according to the present invention is characterized in that upon forming a CVD film on a plurality of semiconductor substrates by using a CVD device that comprises a reaction chamber for forming a CVD film, a first exhaust line which is connected to the above-mentioned reaction chamber and does not include a turbo pump, and a second exhaust line which is connected to the reaction chamber separately from the first exhaust line and which includes a turbo pump, two processes are performed, namely, a first process, which is repeated a number of times that corresponds to a predetermined number of substrates, and which comprises: a step of introducing a semiconductor substrate into the reaction chamber to form a CVD film thereon, and removing the semiconductor substrate, whose film formation is completed, from the chamber, in a state in which, while reactive gas is being supplied to the reaction chamber, the turbo pump is driven to exhaust the reactive gas via the second exhaust line such that the chamber is held at a predetermined internal reaction pressure; and a step of performing high-pressure cleaning of the reaction chamber, from which the semiconductor substrate has been removed, by, while supplying cleaning gas to the reaction chamber, discharging the gas via the second exhaust line by driving the turbo pump at a rotation speed that is lower than the rotation speed during the film formation such that the chamber is held at a predetermined high internal pressure that is higher than the pressure during the above-mentioned film formation; and a second process in which high-pressure cleaning of the inside of the reaction chamber is performed by, while supplying cleaning gas to the reaction chamber, discharging the gas via the first exhaust line such that the chamber is held at a high internal pressure that is equal to the pressure of the first process. The second process for the high-pressure cleaning using the first exhaust line is implemented at least before or after the first process.
The CVD film formation method according to the present invention is further characterized in that upon forming a CVD film on a plurality of semiconductor substrates by using a CVD device that comprises a reaction chamber for forming a CVD film, a first exhaust line which is connected to the reaction chamber and does not include a turbo pump, and a second exhaust line which is connected to the reaction chamber separately from the first exhaust line and which includes a turbo pump, two processes are performed, namely, a first process which is repeated a number of times that corresponds to a predetermined number of substrates, and which comprises: a step of introducing a semiconductor substrate into the reaction chamber to form a CVD film thereon and, removing the semiconductor substrate, whose film formation is completed, from the chamber, in a state in which, while reactive gas is being supplied to the reaction chamber, the turbo pump is driven to exhaust the reactive gas via the second exhaust line such that the chamber is held at a predetermined internal reaction pressure; and a step in which high-pressure cleaning of the inside of the reaction chamber, from which the semiconductor substrate has been removed, is performed by, while supplying cleaning gas to the reaction chamber, discharging the gas via the first exhaust line such that the chamber is held at a predetermined high internal pressure that is higher than the pressure during the film formation; and a second process in which low-pressure cleaning of the inside of the reaction chamber is performed by, while supplying cleaning gas to the reaction chamber, discharging the gas via the second exhaust line such that the chamber is held at a predetermined low internal pressure that is lower than the pressure during the high-pressure cleaning. The second process for the low-pressure cleaning using the second exhaust line is implemented at least before or after the first process.
The pressure during the high-pressure cleaning is preferably greater than 1.5 Torr.
The pressure during the low-pressure cleaning is preferably no less than 0.5 Torr and no more than 1.5 Torr.
The rotation speed of the turbo pump during the high-pressure cleaning is preferably no less than 10000 rpm and no more than 20000 rpm.
The cleaning gas employed during the high-pressure cleaning may be nitrogen trifluoride gas, for example.
The cleaning gas employed during the low-pressure cleaning may be nitrogen trifluoride gas and an inert gas, for example.
The inert gas used may be argon, for example.